Apparatus for recovering hydrocarbons from air-hydrocarbon vapor mixtures

ABSTRACT

An improved process and apparatus for recovering hydrocarbons from an air-hydrocarbon vapor mixture such as the mixture of air and vaporized light hydrocarbon compounds expelled as a result of loading gasoline or the like into storage tanks and tank trucks. The air-hydrocarbon vapor mixture is caused to flow through a bed of solid adsorbent whereby the hydrocarbons are removed from the mixture and a residue gas stream comprised of substantially hydrocarbon-free air is produced. The substantially hydrocarbon-free air is vented to the atmosphere and a second bed of solid adsorbent having hydrocarbons adsorbed thereon is subjected to conditions which cause desorption of the hydrocarbons and thereby regeneration of the bed. The flow pattern of the inlet air-hydrocarbon vapor mixture and the bed of solid adsorbed being regenerated are periodically changed so that when the bed through which the inlet air-hydrocarbon mixture is flowing becomes loaded with adsorbed hydrocarbons, the inlet air-hydrocarbon mixture is caused to flow through the bed which has just been regenerated. The regeneration of the beds is accomplished by evacuating the beds with vacuum pumping whereby a major portion of the hydrocarbons are desorbed therefrom, subsequently introducing a small quantity of heated hydrocarbon-free air into the beds whereby additional hydrocarbons are stripped therefrom and then subjecting the bed to further evacuation by ejector jet pumping while continuing to evacuate the bed by vacuum pumping whereby yet additional hydrocarbons are desorbed therefrom. The air-hydrocarbon vapor mixture produced in the regeneration of the beds is contacted with a liquid absorbent whereby a major portion of the hydrocarbons are absorbed therefrom and recovered. Apparatus for carrying out the process of the invention is also provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process and apparatus for recoveringhydrocarbons from air-hydrocarbon vapor mixtures, and more particularly,but not by way of limitation, to an improved process and apparatus forrecovering vaporized gasoline light ends and the like from a mixturethereof with air expelled from tank trucks and the like.

2. Description of the Prior Art

In handling multicomponent hydrocarbon liquids such as gasoline,kerosene and the like, air-hydrocarbon vapor mixtures are readilyproduced which cannot be vented directly to the atmosphere due to theresulting pollution of the environment and fire and/or explosion hazard.Consequently, a variety of processes and apparatus have been developedand used for removing hydrocarbon vapors from such air-hydrocarbon vapormixtures whereby the remaining air can be safely vented to theatmosphere. The removed hydrocarbons are generally liquefied andrecombined with the hydrocarbon liquid from which they were vaporizedthereby making their recovery economically advantageous.

A process for the recovery of light mixed hydrocarbon vapors from anair-hydrocarbon mixture expelled as a result of storage breathing orloading of a vented hydrocarbon vessel is described in U.S. Pat. No.4,006,423. In accordance with such process, the air-hydrocarbon vapormixture from which hydrocarbons are to be removed and recovered ispassed through a bed of solid adsorbent having an affinity forhydrocarbons. As the mixture passes through the bed, a major portion ofthe hydrocarbons contained in the mixture are adsorbed on the bed and aresidue gas stream is produced which is comprised of substantiallyhydrocarbon-free air. While a first bed of solid adsorbent is adsorbinghydrocarbons from the mixture, a second bed of solid adsorbent havinghydrocarbons adsorbed thereon is regenerated by evacuation. Thecompleteness of the regeneration of the solid adsorption beds of theprocess is dependent solely on the degree of vacuum produced in the bedsby the vacuum pump utilized. Because vacuum pumps are incapable ofachieving total vacuum, i.e., lowering the absolute pressure exerted onthe beds to zero, a quantity of hydrocarbons are left adsorbed on thebeds atter regeneration which reduces the capacity of the beds to adsorbadditional hydrocarbons and reduces the service life of the adsorbent.

The hydrocarbon-rich air-hydrocarbon mixture produced as a result of theregeneration of the bed is contacted with a liquid adsorbent wherebyhydrocarbons are removed therefrom and the residue gas stream from theabsorption step is recycled to the bed through which the inletair-hydrocarbon mixture is flowing. In accordance with the teachings ofU.S. Pat. No. 4,066,423, the liquid absorbent utilized is liquidhydrocarbons condensed from the air-hydrocarbon vapor mixture producedin the evacuation regeneration step. More specifically, thehydrocarbon-rich air-hydrocarbon vapor mixture is cooled wherebyportions of the hydrocarbons are condensed and such condensedhydrocarbons are circulated into contact with the remainingair-hydrocarbon vapor mixture whereby hydrocarbon vapors are absorbed bythe liquids.

Numerous other processes and apparatus for recovering hydrocarbons fromair-hydrocarbon vapor mixtures or otherwise treating said mixtures aredisclosed in U.S. Pat. Nos. 3,897,193; 3,768,232; 3,867,111; 3,455,089;3,543,484; and 3,776,283. In all of the prior processes which utilizesolid adsorbent for removing hydrocarbons from air-hydrocarbon vapormixtures, regeneration of the adsorbent is incomplete wherebyhydrocarbons are left on the adsorbent reducing the capacity, efficiencyand service life thereof.

By the present invention, an improved process is provided which utilizessolid adsorbent for removing hydrocarbons and which achieves a morecomplete regeneration of the adsorbent than can be accompoished by priorprocesses thereby making the process more efficient, more economical tocarry out and increasing the service life of the adsorbent used. Inaddition, by the process of the present invention, a stream of theliquid from which the hydrocarbon vapors originated is used to absorbthe removed hydrocarbons in a simple and economical system therebyobviating the need for condensing the removed hydrocarbons usingelaborate refrigeration or other similar apparatus which is expensive toinstall and operate.

SUMMARY OF THE INVENTION

An improved process for recovering hydrocarbons from an inletair-hydrocarbon vapor mixture comprising flowing the inlet mixturethrough a first bed of solid adsorbent whereby hydrocarbons are adsorbedon the bed and a residue gas stream comprised of substantiallyhydrocarbon-free air which is vented to the atmosphere is produced. Asecond bed of solid adsorbent having hydrocarbons adsorbed thereon isevacuated and thereby regenerated by vacuum pumping whereby a majorportion of the hydrocarbons are desorbed from the bed and ahydrocarbon-rich air-hydrocarbon mixture is produced. The second bed ismore thoroughly regenerated by injection, under high vacuum conditions,of a small quantity of hydrocarbon-free air followed by furtherevacuation by ejector jet pumping whereby additional hydrocarbons aredesorbed from the bed. The hydrocarbon-rich air-hydrocarbon mixtureproduced as a result of the evacuation of the second bed is contactedwith a liquid absorbent whereby a major portion of the hydrocarbons areremoved therefrom and a residue gas stream comprised of air and a minorportion of hydrocarbons is produced. The residue gas stream is combinedwith the inlet air-hydrocarbon mixture whereby it flows through thefirst adsorbent bed and hydrocarbons removed therefrom. The flow patternof the inlet air-hydrocarbon mixture and the bed of solid adsorbentbeing evacuated are periodically changed whereby when the bed throughwhich the inlet air-hydrocarbon mixture is flowing becomes loaded withadsorbed hydrocarbons, the inlet air-hydrocarbon mixture is caused toflow through the bed which has just been evacuated. Apparatus forcarrying out the improved process of this invention is also provided.

It is, therefore, a general object of the present invention to providean improved process and apparatus for recovering hydrocarbons fromair-hydrocarbon vapor mixtures.

A further object of the present invention is the provision of a processand apparatus whereby hydrocarbons contained in an air-hydrocarbonmixture are adsorbed on a bed of solid adsorbent and the bed isregenerated more completely than prior processes.

Yet a further object of the present invention is the provision ofapparatus for recovering hydrocarbons from an air-hydrocarbon vapormixture which is relatively inexpensive to install and operate ascompared to prior apparatus.

Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of preferred embodiments which follows whentaken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing forming a part of this disclosure, apparatus for carryingout the process of this invention is illustrated diagrammatically.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawing, apparatus of the present invention isillustrated and generally designated by the numeral 10. The apparatus 10is comprised of a pair of adsorbers 12 and 14, each of which contains abed of solid adsorbent through which gases can flow. Each of theadsorbers 12 and 14 are closed vessels and include connectionspositioned on opposite sides of the beds of adsorbent contained therein.That is, the adsorber 12 includes inlet and outlet connections 16 and 18and the adsorber 14 includes inlet and outlet connections 20 and 22.While various solid adsorbents having an affinity for hydrocarbons canbe utilized in the adsorbers 12 and 14, activated carbon is preferred inthat it is particularly suitable for adsorbing light hydrocarbon vaporsof the type found in air-hydrocarbon vapor mixtures and for vacuumregeneration.

An air-hydrocarbon vapor mixture inlet header 24 is provided connectedto a conduit 26 which conducts an air-hydrocarbon vapor mixture from asource thereof to the apparatus 10. A pair of conduits 28 and 30 areconnected to the header 24 and to the connections 16 and 20 of theadsorbers 12 and 14, respectively. Conventional switching valves 32 and34 are disposed in the conduits 28 and 30, respectively, and a header 36is connected to the conduits 28 and 30 at points thereon between theswitching valves 32 and 34 and the connections 16 and 20 of theadsorbers 12 and 14. A pair of switching valves 38 and 40 are disposedin the header 36 and a conduit 42 is connected to the header 36 at apoint between the switching valves 38 and 40. A residue gas header 44 isprovided, and a pair of conduits 46 and 48 are connected to the header44 and to the connections 18 and 22 of the adsorbers 12 and 14.Switching valves 50 and 52 are disposed in the conduits 46 and 48,respectively, and a conduit 54 is connected to the header 44 between thevalves 50 and 52 for venting residue gas to the atmosphere. A strippingair header 56 is provided connected to the conduits 46 and 48 at pointsthereon between the switching valves 50 and 52 and the connections 18and 22 of the adsorbers 12 and 14. A pair of check valves 58 and 60 aredisposed in the header 56 and a conduit 62 is connected to the header 56at a point between the valves 58 and 60. An air heater 64 which can takevarious forms and a switching valve 66 are disposed in the conduit 62.The end of the conduit upstream from the switching valve 66 and heater64 is left open to the atmosphere and a conventional air filter (notshown) is generally attached thereto for preventing solid impuritiesfrom entering the adsorbers. The open end of the conduit 54 can alsoinclude a flame arrestor (not shown).

The other end of the conduit 42 connected to the header 36 is connectedto the suction connection of an ejector jet pump 68. The ejector jetpump 68 is of conventional design and includes a jet forming nozzledisposed within a suction chamber and a venturi-shaped diffuser (notshown). A suction connection is provided on the suction chamber, adischarge connection is provided on the end of the diffuser and anoperating stream inlet connection is provided on the nozzle. Inoperation, an operating gas stream is caused to pass through the jetforming nozzle and into the diffuser which creates a suction in thesuction chamber. The conduit 42 is connected to the suction chamberconnection and the discharge connection of the ejector 68 is connectedto a conduit 70. The conduit 70 is in turn connected to the suctionconnection of a vacuum pump 72.

While various types and designs of vacuum pumps can be utilized inaccordance with the present invention, a conventional liquid seal vacuumpump, also known as a liquid ring vacuum pump, is preferred in that sucha pump is capable of producing a high vacuum, is relatively inexpensiveand is much safer in this type of service. The pump utilizes a sealliquid which is circulated through the pump. The seal liquid can beconfined in a closed circuit and cooled which keeps the pump cool andcools the gas or gases flowing through the pump. The presence of theseal liquid in the pump precludes any possibility of explosions sincethe gas cannot approach its auto-ignition temperature nor can sparkingoccur due to mechanical failures within the pump.

The liquid seal vacuum pump 72 includes a suction connection 74 to whichthe conduit 70 is attached, a discharge connection 76 and a seal liquidinlet connection 78 for returning seal liquid thereto. A conduit 80 isconnected to the discharge connection 76 of the pump 72 and to an inletconnection 82 of a separator 84. In a preferred embodiment, an absorber86 is integrally connected to the top of the separator 84, but as willbe understood, the absorber 86 and separator 84 can be separate vessels.

The separator 84 is a three phase separator capable of separating theseal liquid utilized for the pump 72, condensed hydrocarbons and anair-hydrocarbon vapor mixture from each other. Also, in the embodimentillustrated in the drawing, the separator 84 includes a chamber foraccumulating separated condensed hydrocarbon liquids andhydrocarbon-rich liquid absorbent entering the separator 84 from theabsorber 86 whereby such liquids are removed from the separator 84 in acombined state. More specifically, the separator 84 includes a weir 88which divides the separator into a forward compartment 90 and a rearwardcompartment 92. The seal liquid and condensed hydrocarbon liquidsentering the separator 84 by way of the inlet connection 82 areseparated from the air-hydrocarbon vapor mixture in the forwardcompartment 90. The seal liquid is heavier than the condensedhydrocarbon liquids and is immiscible therewith, and consequently, theseal liquid accumulates in the bottom of the forward compartment 90 fromwhere it is removed by way of a seal liquid outlet connection 94attached to the separator 84. Condensed hydrocarbon liquids accumulatingin the compartment 90 spill over the top of the weir 88 into thecompartment 92. Hydrocarbon-rich liquid absorbent from the absorber 86enters the compartment 92 by way of the open bottom of the absorber 86connected to the top of the separator 84 and also accumulates in thecompartment 92. The rich liquid absorbent-condensed hydrocarbon liquidmixture is removed from the separator 84 by way of an outlet connection96. The separated air-hydrocarbon vapor mixture passes from theseparator 84 into the absorber 86 by way of the connection therebetween.

A conduit 98 is connected to the seal liquid outlet connection 94 of theseparator 84 and to the seal liquid inlet connection 78 of the pump 72.A cooler 100 is disposed in the conduit 98 for cooling the seal liquidas it flows therethrough. In certain situations a seal fluid circulationpump can be disposed in the conduit 98 between the separator 84 and thecooler 100. While the cooler 100 can be of various types and designs, aheat exchanger which cools the seal liquid by passing it in heatexchange relationship with a stream of lean liquid of the samecharacteristics as that used as the absorption medium in the absorber 86is preferred and generally is the most economical.

A conduit 102 is connected to the connection 96 of the separator 84 andto a rich liquid absorbent-condensed hydrocarbon liquids pump 104. Thedischarge connection of the pump 104 is connected to a conduit 106 whichleads the rich liquid absorbent-condensed hydrocarbon liquids mixture toa storage facility (not shown). It is preferred that designated facilityfor storage of the rich liquid absorbent be distinct from that for thelean liquid absorbent to insure lowest possible vapor pressure of thelean liquid absorbent thereby insuring optimum system performanceefficiency.

The absorber 86 includes means disposed therein for bringing aboutintimate contact between a liquid absorbent flowing downwardly thereinand a vapor mixture flowing upwardly therein. Such means can becomprised of vapor-liquid contact trays or any of a variety ofconventional packing material. Preferably, the absorber 86 includes asection of packing material 108 disposed in the top portion thereof forbringing about such intimate contact. A residue gas outlet connection110 and a lean liquid absorbent inlet connection 112 are provided abovethe packed section 108. As described above, in the embodiment shown inthe drawing, the open bottom of the absorber 86 is sealingly connectedto the top of the separator 84 over an opening in the separator 84whereby rich liquid absorbent produced in the absorber 86 flowsdownwardly out of the absorber and into the separator 84. In a likemanner, the mixture of air and hydrocarbons separated in the separator84 flows upwardly to the open bottom of the absorber into contact withthe liquid absorbent flowing downwardly therein whereby hydrocarbons areabsorbed and removed from the vapor mixture and a residue gas streamcomprised of air and a minor portion of hydrocarbons is produced.

A conduit 114 is connected to the lean liquid absorbent inlet 112 of theabsorber 86 and to the discharge connection of a pump 116. A conduit 118is connected to the suction connection of the pump 116 which leads astream of lean liquid absorbent from a source thereof such as a storagetank to the pump 116. As indicated above, a conduit 126 can be providedto connect conduit 114 with cooler 100 whereby a slip stream of leanliquid absorbent can flow to an inlet connection 132 of the separator 84by way of a conduit 128.

In certain cases, the lean liquid absorbent may be too warm to usedirectly as an absorbent and seal fluid coolant. In such cases, anexchanger (not shown) can be disposed in conduit 114 for cooling thelean liquid absorbent with an appropriate cooling medium such as coolingwater, refrigerant, etc.

The residue gas stream produced in the absorber 86 exits the absorber byway of the connection 110 thereof and flows into a conduit 120 connectedthereto and connected to the inlet air-hydrocarbon vapor header 24. Aconduit 122 is connected to the conduit 120 and to the jet formingnozzle inlet connection of the ejector 68. A switching valve 124 isdisposed in the conduit 122.

As will be understood by those skilled in the art, the switching valves32, 34, 38, 40, 50, 52, 66 and 124 can be operated manually, but arepreferably automatically operated valves which are controlled by aconventional cycle controller. The length of each cycle, i.e., theperiod of time between when the switching valves are operated can becontrolled by a timer or other instrument sensing one or more variablesin the operation of the apparatus 10, such as the degree of vacuumachieved in the absorbent bed being regenerated, the composition of thegas stream being vented to the atmosphere, etc.

Operation of the Apparatus 10

In operation of the apparatus 10, the switching valves 32, 34, 38, 40,50 and 52 and operated in a manner whereby the inlet air-hydrocarbonvapor mixture is caused to flow through one of the adsorbers 12 or 14while the other of the adsorbers is being regenerated. For example,during a first cycle, the switching valve 32 is open and the switchingvalve 34 closed whereby the inlet air-hydrocarbon vapor mixture flowsinto the adsorber 12 by way of the conduit 28, switching valve 32 andconnection 16 of the adsorber 12. Because the switching valve 34disposed in the conduit 30 is closed, the inlet air-hydrocarbon vapormixture is prevented from entering the adsorber 14. The switching valve50 disposed in the conduit 46 is open and the switching valve 52disposed in the conduit 48 is closed whereby the residue gas streamproduced in the adsorber 12 exits the adsorber 12 by way of theconnection 18 thereof, the conduit 46 and the switching valve 50 andenters the header 44. From the header 44, the residue gas stream flowsthrough the conduit 54 from where it is vented to the atmosphere. Theswitching valve 38 disposed in the header 36 is closed and the switchingvalve 40 disposed therein is open whereby the adsorbent bed within theadsorber 14 is communicated with the suction connection 74 of the vacuumpump 72 by way of the connection 20 of the adsorber 14, the header 36,the open switching valve 40, the conduit 42, the ejector 68 and theconduit 70. The switching valves 66 and 124 disposed in the conduits 62and 122, respectively, are initially closed.

During the first part of the cycle when the switching valves are in themode described above, the inlet air-hydrocarbon vapor mixture flowsthrough the bed of adsorbent within the adsorber 12 whereby hydrocarbonsare adsorbed on the bed and removed from the mixture. The residue gasproduced which is comprised of substantially hydrocarbon-free air isvented to the atmosphere by way of the air vent 54. Simultaneously, thebed of adsorbent disposed within the adsorber 14 is evacuated by theliquid seal vacuum pump whereby hydrocarbons are desorbed therefrom. Ahydrocarbon-rich air-hydrocarbon vapor mixture is withdrawn from theadsorbent bed within the adsorber 14 which flows through the vacuum pump72. Cooled seal liquid, preferably water or a mixture of water and asubstance which functions as an antifreeze agent in the winter and as anagent to lower seal fluid vapor pressure in the summer, e.g., ethyleneglycol, flows into the vacuum pump 72 by way of the connection 78thereof and is discharged by way of the discharge connection 76 with theair-hydrocarbon vapor mixture. The intimate contact of theair-hydrocarbon vapor mixture with the cool seal liquid while flowingthrough the vacuum pump 72 cools the vapor mixture and causes heavyhydrocarbons contained therein to be condensed. Thus, a stream ofhydrocarbon-rich air-hydrocarbon vapor mixture containing both sealliquid and condensed hydrocarbon liquids exits the pump 72 and flowsthrough the conduit 80 into the separator 84. While passing through theseparator 84, the air-hydrocarbon vapor mixture, seal liquid andcondensed hydrocarbon liquids are separated from each other. Aspreviously described, the separated seal liquid flows from the separator84 by way of the connection 94 thereof, the conduit 98 and the cooler100 back into the vacuum pump 72. Thus, the seal liquid is continuallycirculated between the pump 72, the separator 84 and the cooler 100while the pump 72 is operating.

The separated condensed hydrocarbon liquids spill over the weir 88 andflow into the compartment 92 of the separator 84 where they combine withrich liquid absorbent flowing into the compartment 92 from the absorber86 and removed therefrom by way of the connection 96 thereof, theconduit 102 and the pump 104. From the pump 104, the rich liquidabsorbent-condensed hydrocarbon liquids mixture is conducted by way ofthe conduit 106 to storage facilities or a point of further processing(not shown).

A stream of lean liquid absorbent is pumped from a source thereof by thepump 116 and flows by way of the conduit 130, conduit 114 and connection112 into the absorber 86. The lean liquid absorbent flows downwardlywithin the absorber 86 through the packed section 108 thereof andintimately contacts the separated air-hydrocarbon mixture flowingupwardly therethrough from the separator 84. As the air-hydrocarbonvapor mixture is contacted by the liquid absorbent, hydrocarbons areabsorbed by the liquid absorbent and removed from the vapor mixturewhereby a residue gas stream comprised of air and a minor portion ofhydrocarbons is produced. The residue gas stream exits the absorber 86by way of the connection 110 thereof and flows by way of the conduit 120into the header 24 where it combines with the inlet air-hydrocarbonvapor mixture and flows through the adsorber 12. As will be understood,the hydrocarbons contained in the residue gas stream are adsorbed on thebed of adsorbent within the adsorber 12 along with hydrocarbons from theinlet air-hydrocarbon vapor mixture.

During a latter part of the cycle, after a major portion of hydrocarbonsadsorbed on the bed of adsorbent within the adsorber 14 have beendesorbed therefrom by the operation of the vacuum pump 72, i.e., theinitial evacuation of the adsorber 14, the switching valve 66 in theconduit 62 is opened whereby a relatively small quantity ofhydrocarbon-free air from the atmosphere enters the conduit 62, flowsthrough the heater 64 so that it is heated and then flows by way of theheader 56, the check valve 60 and the connection 22 of the adsorber 14into the adsorber 14. The heated hydrocarbon-free air flows through thebed of adsorbent contained in the adsorber 14 and is withdrawn therefromby the vacuum pump 72 as previously described. The introduction of aquantity of heated hydrocarbon-free air into the adsorbent bed containedwithin the adsorber 14 functions to strip additional hydrocarbons fromthe bed which were not desorbed therefrom by vacuum pumping, i.e., bythe lowering of the pressure exerted on the bed to the degree of vacuumachieved by the vacuum pump 72.

Simultaneously with or after the required quantity of heated air hasbeen introduced into the adsorber 14 to strip additional hydrocarbonstherefrom the switching valve disposed in the conduit 62 is closed andthe switching valve 124 disposed in the conduit 122 is opened. Theopening of the switching valve 124 causes a portion of the residue gasstream produced in the absorber 86 to flow by way of the conduit 122through the jet forming nozzle of the ejector 68 and into the vacuumpump 72. The jet of vapors flowing through the ejector 68 causes asuction to be produced which is in addition to the suction produced bythe vacuum pump 72 exerted on the bed of adsorbent within the adsorber14 which evacuates the adsorber further and causes additionalhydrocarbons to be desorbed therefrom.

Thus, as will be apparent, the combination of initially evacuating theadsorber 14 by vacuum pumping, stripping the adsorbent bed with heatedhydrocarbon-free air and then further evacuating the adsorbent bedbrings about the regeneration of the bed to a greater degree than ispossible by vacuum pumping alone. This more complete regeneration of thebed increases the capacity of the bed to adsorb additional hydrocarbons,increases the overall efficiency of the apparatus 10 and increases theservice life of the adsorbent.

After the adsorbent bed within the adsorber 14 has been fullyregenerated and the adsorbent bed within the adsorber 12 loaded withhydrocarbons from the air-hydrocarbon vapor mixture flowingtherethrough, the switching valve 124 in the conduit 122 is closed, theswitching valve 66 is caused to remain closed and the other switchingvalves of the apparatus 10 are reversed. That is, the switching valves32 and 50 are closed, the switching valves 34 and 52 are opened, theswitching valve 38 is opened and the switching valve 40 is closed. Thiscauses the flow pattern of the inlet air-hydrocarbon vapor mixture to bechanged whereby the mixture flows through the regenerated adsorbent bedwithin the adsorber 14 and the residue gas therefrom to be vented to theatmosphere. The adsorbent bed within the adsorber 12 is simultaneouslycommunicated with the vacuum pump 72 whereby it is evacuated and theswitching valves 66 and 124 are opened during a latter part of the cycleas described above to strip the adsorbent bed within the adsorber 12 andfurther evacuate the adsorbent bed whereby additional hydrocarbons aredesorbed therefrom.

As will be understood by those skilled in the art, the flow pattern ofthe inlet air-hydrocarbon vapor mixture and the bed being regeneratedare continuously changed or cycled whereby when the adsorbent bedthrough which the inlet vapor mixture is flowing becomes loaded withadsorbed hydrocarbons, the inlet mixture is caused to flow into the bedwhich has just been regenerated. The hydrocarbon-rich air-hydrocarbonmixture produced from the bed being regenerated is continuouslycontacted with liquid absorbent in the absorber 86 whereby thehydrocarbons are recovered.

The apparatus 10 is particularly suitable for recovering vaporizedgasoline light ends mixed with air produced as a result of loadinggasoline into tank trucks and other vessels. In this application, theair-gasoline vapor mixture is processed in the apparatus 10 is describedabove and the liquid absorbent utilized is gasoline. That is, storedgasoline is pumped from a storage facility into the absorber 86 and therich gasoline and condensed hydrocarbon liquids produced by theapparatus 10 are returned to the gasoline storage facility. Because thestored gasoline is continuously being loaded out of the storagefacilities and replaced by newly produced gasoline, the stream ofgasoline pumped to the absorber is lean enough to efficiently absorbgasoline light ends.

In order to more clearly illustrate the operation of the apparatus 10,the following example is given.

EXAMPLE

A typical gasoline truck loading terminal has the following loadingpattern:

    ______________________________________                                        Maximum Instantaneous Rate                                                                          2200 gallons/minute                                     Maximum Throughput in 15 Minutes                                                                    16500 gallons                                           Maximum Throughput in 1 Hour                                                                        48000 gallons                                           Maximum Throughput in 4 Hours                                                                       168000 gallons                                          Maximum Throughput Daily                                                                            960000 gallons                                          ______________________________________                                    

The gasoline loaded is deemed to have the following properties:

    ______________________________________                                        Summer:        10 psia RVP, 75° F. maximum                             Winter:        14 psia RVP, 10° F. minimum                             ______________________________________                                    

It is recognized that the hydrocarbon concentration of theair-hydrocarbon vapor generated by loading gasoline into the trucktransports will vary according to gasoline volatility and the degree ofair saturation attained.

Based on the above gasoline properties and other experience factorsknown to those skilled in the art, a design hydrocarbon concentration of35 Vol.% is selected.

The apparatus 10 is designed for an approximately 15 minute cycle time,and consequently, it is necessary to design each adsorption vessel 12and 14 to handle a net air-hydrocarbon vapor influent from the truckloading rack of 353 cubic feet per minute and 2647 cubic feet each cyclebased on a 1.2 vapor growth factor. Approximately 9000 lbs. of theappropriate activated carbon is chosen and distributed equally in two 7feet in diameter by approximately 8 feet high adsorption vessels 12 and14. These two adsorption vessels are operated near ambient temperaturesand only slightly above atmospheric pressure during the adsorptioncycle.

A liquid ring vacuum pump 72 with a 30 horsepower electric motor isprovided for regeneration of the beds of carbon after each adsorptioncycle. Very effective regeneration of carbon beds 12 and 14 isaccomplished each cycle by the introduction, under high vacuumconditions, of approximately 30 standard cubic feet of air heated to200° to 300° F. The regeneration apparatus provided allows attainment of49 millimeters of mercury absolute pressure each cycle with the vacuumpump 72 alone and with the vacuum assist ejector 68 an absolute pressureof 12 millimeters of mercury or less can easily be attained.

To accomplish the objective of recovery, concentrated hydrocarbon vaporscontaining only 5 to 20 Vol.% air are discharged from the vacuum pump 72to a 2 feet diameter by approximately 12 feet high packed absorptioncolumn 86 integrally connected to a 3.5 feet diameter by approximately 8feet long separator 84, where the major portion of the hydrocarbonvapors are absorbed and thereby recovered into a downward flowing streamof gasoline.

The minor portion of hydrocarbon vapors not immediately absorbed intothe gasoline absorbent exits the top of the absorber 86. Thesehydrocarbons flow to whichever adsorber 12 or 14 is in the adsorptionmode where they are adsorbed onto the activated carbon. Subsequently,during regeneration of the carbon, they are removed returning to theabsorber 86. Eventually almost all of the hydrocarbon vapors arerecovered.

Centrifugal pumps 104 and 116 each with 5 horsepower electric motordrivers are provided to circulate 125 gallons per minute of gasolinefrom storage facilities for purposes of providing the absorption mediumin the absorber 86 and to provide the necessary seal fluid coolingmedium in the seal fluid cooler 100.

Apparatus 10 designed as described above can be expected to remove andrecover the hydrocarbon vapors generated from the transport loading racksuch that less than 10 milligrams of hydrocarbons will be vented to theatmosphere per liter of gasoline loaded.

Thus, the present invention is well adapted to carry out the objects andattain the ends and advantages mentioned as well as those inherenttherein. While presently preferred embodiments of the invention havebeen described for purposes of this disclosure, numerous changes in thearrangement of process steps and apparatus elements will suggestthemselves to those skilled in the art, which changes are encompassedwithin the spirit of this invention as defined by the appended claims.

What is claimed is:
 1. Apparatus for recovering hydrocarbons from anair-hydrocarbon vapor mixture comprising:(a) a pair of adsorberscontaining beds of solid adsorbent having an affinity for hydrocarbonsand having first and second connections on opposite sides of said beds;(b) first conduit means connected to the first connections of saidadsorbers for conducting said air-hydrocarbon vapor mixture to saidadsorbers and for evacuating said adsorbers; (c) valve means disposed insaid first conduit means for selectively causing said air-hydrocarbonvapor mixture to flow through one or the other of said adsorbers; (d)second conduit means connected to the second connections of saidadsorbers for conducting residue gas exiting said adsorbers to theatmosphere; (e) second valve means disposed in said second conduit meansfor selectively causing the second connections of one or the other ofsaid adsorbers to be open to the atmosphere; (f) a vacuum pump having asuction connection and a discharge connection; (g) third conduit meansconnected between the suction connection of said vacuum pump and thefirst conduit means connected to said adsorbers; (h) third valve meansdisposed in said third conduit means for selectively communicating oneor the other of said adsorbers with the suction connection of saidvacuum pump; (i) an ejector jet pump having a suction connection, adischarge connection and a gas jet inlet connection, said ejector jetpump being disposed in said third conduit means with the suction anddischarge connections thereof being connected to said third conduitmeans; (j) an absorber for contacting an air-hydrocarbon vapor mixturewith a liquid absorbent having an air-hydrocarbon vapor mixture inletconnection, a residue gas outlet connection, a lean liquid absorbentinlet connection and a rich liquid absorbent outlet connection; (k)fourth conduit means connected between the air-hydrocarbon vapor mixtureinlet of said absorber and the discharge connection of said vacuum pump;(l) fifth conduit means connected between the residue gas outletconnection of said absorber and said first conduit means; (m) sixthconduit means connected between said fifth conduit means and the gas jetinlet connection of said ejector jet pump; and (n) fourth valve meansdisposed in said sixth conduit means for selectively communicating saidfifth conduit means with the gas jet inlet connection of said ejectorjet pump.
 2. The apparatus of claim 1 which is further characterized toinclude:seventh conduit means connected to said second conduit means forconducting air from the atmosphere to said adsorbers by way of saidsecond connections thereof; and fifth valve means disposed in saidseventh conduit means for selectively communicating one or the other ofsaid adsorbers with air from the atmosphere.
 3. The apparatus of claim 2which is further characterized to include means for heating air disposedin said seventh conduit means.
 4. The apparatus of claim 3 which isfurther characterized to include means for cooling an air-hydrocarbonvapor mixture disposed in said fourth conduit means.
 5. The apparatus ofclaim 1 wherein said vacuum pump is a liquid seal vacuum pump having asuction connection, a discharge connection and a seal liquid inletconnection and said apparatus is further characterized to include:aseparator for separating an air-hydrocarbon vapor mixture, condensedhydrocarbon liquids and seal liquid from each other and combining richliquid absorbent with condensed hydrocarbon liquids having anair-hydrocarbon vapor-condensed hydrocarbon liquids-seal liquid inletconnection, a rich liquid absorbent inlet connection, a seal liquidoutlet connection, a rich liquid adsorbent-condensed hydrocarbon liquidoutlet connection and an air-hydrocarbon vapor mixture outletconnection, the inlet connection of said separator being connected tosaid fourth conduit means and the air-hydrocarbon vapor mixture outletconnection thereof being connected to the air-hydrocarbon vapor mixtureinlet connection of said absorber; eighth conduit means connectedbetween the seal liquid outlet connection of said separator and the sealliquid inlet connection of said liquid seal vacuum pump; means forcooling seal liquid disposed in said eighth conduit means; and ninthconduit means connected between the rich liquid absorbent inletconnection of said separator and the rich liquid absorbent outletconnection of said absorber.
 6. The apparatus of claim 5 which isfurther characterized to include:tenth conduit means connected to thelean liquid absorbent inlet connection of said absorber and to a sourceof lean liquid absorbent; and a lean liquid absorbent pump disposed insaid tenth conduit means.
 7. The apparatus of claim 6 wherein said meansfor cooling seal liquid is a seal liquid-lean liquid absorbent heatexchanger connected to said eighth and tenth conduit means.
 8. Theapparatus of claim 7 which is further characterized to include:eleventhconduit means connected to the rich liquid absorbent-condensedhydrocarbon liquids outlet connection of said separator and to a liquidabsorbent storage vessel; and a rich liquid absorbent-condensedhydrocarbon liquids pump disposed in said eleventh conduit means.